Portage Lake
Portage Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 7 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 5.9 µg/L.
- Clarity
- 7 ft
- Mean depth
- ~11 ft est.
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- No
Next lake in Cass County
Portage Lake is a mesotrophic lake in Cass County, Minnesota with an estimated average depth of about 11 feet. Water quality is graded A based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 103 other monitored lakes in Cass County, Portage Lake ranks #18 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-23. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 7 ft. Phosphorus level: 20 µg/L. Chlorophyll-a: 5.9 µg/L. Trophic State Index: 48.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | 5.9 µg/L | Good |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Portage Lake
Compare lakeside cabins, hotels, and vacation rentals near Portage Lake in Cass County, Minnesota — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~11 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Portage Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Portage Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Portage Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Aquatic Plant Report — Portage (1650)Aquatic Plant Report · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.016 m/yr | 6 |
| Phosphorus | → Stable | -0.33 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.81 µg/L/yr | 6 |
County Ranking
Ranked #18 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Portage Lake
What is the water quality grade for Portage Lake?
- Portage Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 7 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 5.9 µg/L.
Is Portage Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Portage Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 5.9 µg/L. Always check local health department advisories before swimming.
How deep is Portage Lake?
- No published bathymetric survey covers Portage Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 11 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
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Where this data comes from
30 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA30 samples · 2023–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder